Complex trauma of the upper limb is a common consequence of involvement in serious accidents. Loss of substance including nerve, bone, tendons and vascular defects are challenging surgical issues. A 27- year-old male presented with complex upper limb trauma and loss of a proximal third of the posterior forearm structure as well as loss of active finger extension, ulnar and radial nerve territory anesthesia and ulnar fracture. A composite nerve-tendon-muscle-skin gracilis free flap was retrieved from the contralateral leg, related to tendon transfer of BR to ELP, to supply active hand extension. The patient was required to adhere to intensive post-surgical rehabilitation and monitored for a 3-year follow-up period. Our assessment revealed adequate skin trophism and sufficient muscle strength recovery against resistance (M5). The functional flap associated with tendon transfer was considered an efficient procedure for the management of a complex trauma with loss of posterior interosseous nerve and bone exposition. The free re-innervated gracilis flap may be used to repair complex soft tissue defects with exposed bone and to restore finger extension following severe forearm injuries.